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Nile tilapia is an exotic species produced in Brazilian aquaculture. The aim of this study was to constitute a pathological diagnosis in Oreochromis sp. with a noticeable presence in a river in southern Brazil, and to verify the origin of these fish in this natural habitat, an environment with high sanitary precariousness due to discharges of industrial effluents. A total of 30 fish were collected during three sampling events and their health status was assessed by parasitological fauna survey, parasitological indices and histopathological examination of the gills, liver, spleen and kidney. Five species of monogenea were identified infesting gills and stomach: Cichlidogyrus sclerosus , C. halli , C. thurstonae , Scutogyrus longicornis and Enterogyrus cichlidarum ; and 4 species of trichodinidae infesting the body surface and gills: Trichodina magna , T. compacta , T. centrostrigeata and Paratrichodina africana . The results showed differences according to the seasonality of the collection, with higher parasite count and larger tissue alterations in summer. Histopathological analysis fluctuated from moderate to severe, but necrosis prevailed in all organs and in all fish, indicating that these fish did not enjoy full health., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest., (© Indian Society for Parasitology 2019.)

The present study aimed to contribute to the monogenean dactylogyrids that occur in C. auratus from an ornamental fish farm in southern Brazil. Samples of goldfish were obtained from a fish farm and the gills were removed and analysed to identify the species of Dactylogyrus to determine the levels of infestation. Three species of Dactylogyrus were found in the gills: Dactylogyrus anchoratus , Dactylogyrus baueri and Dactylogyrus formosus . The most prevalent species was D. baueri [prevalence ( P ) = 70%, mean intensity (MI) = 2.14 ± 1.21, mean abundance (MA) = 1.5 ± 1.43], followed by D. anchoratus ( P  = 60%, MI = 1.67 ± 0.81, MA = 1.00 ± 1.05) and D. formosus ( P  = 30%, MI = 1.66 ± 1.15, MA = 0.5 ± 1.64). Dactylogyrus anchoratus shares morphological characteristics with D. arcuatus by the similarity in shape of the haptor parts. Dactylogyrus baueri shows similarity to D. dulkeiti in relation to the pair of anchors and accessory piece of the male copulatory complex. Dactylogyrus formosus presents an accessory piece with branch and total length of the anchors smaller than D. anchoratus . This study reports the occurrence of D. anchoratus , D. baueri and D. formosus in goldfish cultured in southern Brazil. These monogenean species have been described in cyprinid fishes that have a wide geographic distribution with the result of the dissemination of the host in the world., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest.

The toxicity of formalin on Cyprinus carpio var. koi and its anti-parasite effects against Dactylogyrus minutus (Monogenea) in in vitro tests is analyzed. Specimens of D. minutus were submitted to eight concentrations of formalin: 50, 75, 100, 125, 150, 175, 200, 250 mg L -1 , in triplicate. Concentrations of formalin 100, 150 and 200 mg L -1 were then tested to determine the median lethal concentration of 50% of the fish per immersion bath. Fish behavior was also observed during the first 6 h of exposure. The 200 mg L -1 concentration was the most rapid efficacy for D. minutus , killing all parasites in 16 min. All parasites were killed in 47 min at concentration 100 mg L -1 . Concentration 200 mg L -1 was the most lethal for fish in less than 24 h exposure, with 24 h LC 50 at 135.44 (119.78-153.14) mg L -1 . The therapeutic index was 2.05-30 min and 1.15-16 min. A short bath (1 h) is recommended in koi carp with a minimum concentration of 75 mg L -1 of formalin, not exceeding 100 mg L -1 for treatment against D. minutus., Competing Interests: The authors declare that they have no conflict of interest.All procedures were performed following protocols by the Ethics Committee of the Federal University of Santa Catarina (CEUA/UFSC/PP00928).